1. Field of the Invention
The present invention relates to precision surface plates, and more specifically to a precision surface plate supporting variable-temperature operation.
2. Prior Art
Conventional surface plates have a reference plane with an appropriately finished smooth surface, on which a workpiece is machined and measured. When a workpiece is machined, the workpiece, a table, and a processing machine are placed on the surface plate. When a workpiece is measured, the workpiece, a table, and a measuring apparatus are placed on the surface plate.
The normal requirements for these surface plates include lightweight, high specific rigidity, and high temperature stability. A variety of surface plates have been developed to meet those requirements, such as a surface plate for optics, using a carbon-fiber-reinforced composite material formed by the impregnation of carbon fibers with a resin (Japanese Unexamined Patent Application Publication No. Hei-6-331870). This surface plate for optics has achieved high rigidity by using a honeycomb material bonded between two sheets of carbon-fiber-reinforced composite material.
Recent surface plates are required to support variable-temperature operation. Conventional surface plates may meet this requirement as follows, for instance: After the temperature of a whole workshop is changed through the variable-temperature operation controlled by a temperature controller, the temperature characteristics of a workpiece may be measured. After the temperature of the whole workshop is controlled to different temperatures, the temperature characteristics of a checking gauge, such as the linear expansion coefficient, may be obtained by measuring the dimensions of the workpiece at each temperature. If the workshop is not at a reference temperature, the whole workshop is controlled to the reference temperature through variable-temperature operation controlled by the temperature controller, then the workpiece may also be machined or measured.
An important point of the variable-temperature operation is ability to quickly change to a desired temperature. One conventional surface plate meets this requirement by changing the temperature of the surface plate itself, not changing the temperature of the whole workshop. The surface plate includes a high-thermal-conductivity solid metal plate, an electronic cooler provided under the metal plate, a temperature sensor provided inside the metal plate, and a temperature controller for controlling the operation of the electronic cooler in accordance with temperature information from the temperature sensor so that the metal plate is brought to a certain temperature (Japanese Utility Model Registration Application Publication No. Hei-7-38901).
The conventional surface plates described above, however, may not provide satisfactory workpiece machining precision or measurement precision in variable-temperature operation.
The conventional surface plates require an electronic cooler and a temperature sensor for temperature control, and such a complicated configuration can surely be improved.
Accordingly, in addition to lightweight, high specific rigidity, and high temperature stability, a simple configuration ensuring support for variable-temperature operation has recently become an important requirement of surface plates.